PROJECT SUMMARY Evidence-based programs (EBPs) delivered in school settings show great promise in reducing risk for the development of emotional and behavioral disorders (EBDs) among elementary-aged children. However, efforts to sustain EBPs in school settings face a number of barriers. Improving EBP sustainment in schools thus represents a public health priority, but very little research exists to inform the development of sustainment strategies. In order to address this gap, and build a foundation for sustainment strategy development, the specific factors that predict sustainment need to be identified. To achieve this goal, the proposed project will accomplish three primary aims: (1) Determine if malleable teacher (self-efficacy, burnout, attributions), intervention (usability), and school (climate, classroom atmosphere, classroom-level adversity) factors predict EBP treatment fidelity (adherence, competence) and modifications to EBPs (fidelity-consistent, fidelity- inconsistent) during implementation or sustainment; (2) Assess the impact of EBP treatment fidelity and EBP modifications on child outcomes (disruptive behavior problems, social skills) during implementation and sustainment; and (3) Explore the mechanisms through which teacher, intervention, and school factors influence sustainment outcomes. This project builds on a 4-year, federally-funded randomized controlled trial evaluating BEST in CLASS, an effective, teacher-delivered intervention for K-3rd grade children at risk for EBDs. The sample will include 96 teachers, 384 children, and 12 elementary schools in diverse communities located in VA and FL. During the implementation phase, the teachers randomized to BEST in CLASS will receive a one-day training followed by 14 weekly sessions of practice-based coaching. To achieve study aims, a multilevel, interrupted time series design will be used to examine the relation between baseline factors, treatment fidelity (adherence and competence to the core BEST in CLASS practices), modifications (fidelity- consistent, fidelity-inconsistent), and child outcomes (disruptive behavior, social skills), followed by a mixed method approach to elucidate the mechanisms that influence sustainment outcomes. Independent observers will use a gold-standard, observer-rated measure with strong psychometric properties to rate treatment fidelity and modifications to BEST in CLASS at 8 timepoints during implementation (baseline, 4 weeks, 8 weeks, post- intervention [14 weeks]) and sustainment (baseline, 4 weeks, 8 weeks, 14 weeks). Our long-term goal, consistent with NIMH Strategic Priority 4 to strengthen the public health impact of funded research, is to engage in research to maximize the sustainment of EBPs in school settings and thus improve outcomes for children. This R01 is a critical building block in our effort to realize the promise of EBPs and will help us create the blueprint for a strategy designed to improve EBP sustainment in schools that we can develop with a NIMH R34 proposal and subsequently evaluate with a R01 proposal.